Congestive heart failure (CHF), which is often associated with an enlargement of the heart, is a leading cause of death. As a result, the market for the treatment of CHF is becoming increasingly prevalent. For instance, the treatment of CHF is a leading expenditure of Medicare and Medicaid dollars in the United States. Typically, the treatment of CHF enables many who suffer from CHF to enjoy an improved quality of life.
Referring initially to FIG. 1A, the anatomy of a heart 10, specifically the left side of the heart 10, includes a left atrium (LA) 12 and a left ventricle (LV) 14. An aorta 16 receives blood from left ventricle 14 through an aortic valve 18, which serves to prevent regurgitation of blood back into left ventricle 14. A mitral valve 20 is positioned between left atrium 12 and left ventricle 14, and allows one-way flow of blood from the left atrium 12 to the left ventricle 14.
Mitral valve 20, which will be described below in more detail, includes an anterior leaflet 22 and a posterior leaflet 24 that are coupled to cordae tendonae 26 which serve as “tension members” that prevent the leaflets 22, 24 of mitral valve 20 from going past their closing point and prolapsing back into the left atrium. When left ventricle 14 contracts during systole, cordae tendonae 26 limit the upward (toward the left atrium) motion of the anterior and posterior leaflets past the point at which the anterior and posterior leaflets 22, 24 meet and seal to prevent backflow from the left ventricle to the left atrium (“mitral regurgitation” or “mitral insufficiency”). Cordae tendonae 26 arise from a columnae carnae or, more specifically, a musculi papillares (papillary muscles) 28 of the columnae carnae. In various figures herein, some anatomical features have been deleted solely for clarity.
FIG. 1B is a cut-away top-view representation of mitral valve 20 and aortic valve 18. Anterior leaflet 22 and posterior leaflet 24 of the mitral valve 20 are generally thin, flexible membranes. When mitral valve 20 is closed (as shown in FIG. 1B), anterior leaflet 22 and posterior leaflet 24 are generally aligned and contact one another along a “line of coaptation” several millimeters back from their free edges, to create a seal that prevents mitral regurgitation. Alternatively, when mitral valve 20 is opened, blood flows downwardly through an opening created between anterior leaflet 22 and posterior leaflet 24 into left ventricle 14.
Many problems relating to mitral valve 20 may occur and may cause many types of ailments. Such problems include, but are not limited to, mitral regurgitation. Mitral regurgitation, or leakage, is the backflow of blood from left ventricle 14 into the left atrium 12 due to an imperfect closure or prolapse of mitral valve 20. That is, leakage often occurs when the anterior and posterior leaflets to not seal against each other, resulting in a gap 32 between anterior leaflet 22 and posterior leaflet 24.
In general, a relatively significant gap 32 may exist between anterior leaflet 22 and posterior leaflet 24 (as shown in FIG. 1C) for a variety of different reasons. For example, a gap 32 may exist due to congenital malformations, because of ischemic disease, or because the heart 10 has been damaged by a previous heart attack. A gap 32 may also be created when congestive heart failure, e.g., cardiomyopathy, or some other type of distress which causes a heart to be enlarged. Enlargement of the heart can result in dilation (stretching) of the mitral annulus. This enlargement is usually limited to the posterior valve annulus and is associated with the posterior leaflet, because the anterior annulus is a relataively rigid fibrous structure. When the posterior annulus enlarges, it causes the posterior leaflet to move away from the anterior leaflet, causing a gap because the two leaflets no longer form proper coaptation, and this results in leakage of blood through the valve, or regurgitation.
Leakage through mitral valve 20 generally causes a heart 10 to operate less efficiently, as the heart 10 must pump blood both out to the body via the aorta, and also back (in the form of mitral regurgitation) back into the left atrium. Leakage through mitral valve 20, or general mitral insufficiency, is thus often considered to be a precursor to CHF or a cause of progressive worsening of heart failure. There are generally different levels of symptoms associated with heart failure. Such levels are classified by the New York Heart Association (NYHA) functional classification system. The levels range from a Class 1 level which is associated with an asymptomatic patient who has substantially no physical limitations to a Class 4 level which is associated with a patient who is unable to carry out any physical activity without discomfort, and has symptoms of cardiac insufficiency even at rest. In general, correcting or reducing the degree of mitral valve leakage may be successful in allowing the NYHA classification grade of a patient to be reduced. For instance, a patient with a Class 4 classification may have his classification reduced to Class 3 or Class 2 and, hence, be relatively comfortable at rest or even on mild physical exertion. By eliminating the flow of blood backwards into the left atrium, therapies that reduce mitral insufficiency reduce the work load of the heart and may prevent or slow the worsening of heart function and congestive heart failure symptoms that is common when a significant degree of mitral insufficiency remains uncorrected.
Treatments used to correct for mitral valve leakage or, more generally, CHF, are typically highly invasive, open-heart surgical procedures as described below. In extreme cases, this may include implantation of a ventricular assist device such as an artificial heart in a patient whose own heart is failing. The implantation of a ventricular assist device is often expensive, and a patient with a ventricular assist device must be placed on extended anti-coagulant therapy. As will be appreciated by those skilled in the art, anti-coagulant therapy reduces the risk of blood clots being formed, as for example, within the ventricular assist device. While reducing the risks of blood clots associated with the ventricular assist device is desirable, anti-coagulant therapies may increase the risk of uncontrollable bleeding in a patient, e.g., as a result of a fall, which is not desirable.
Rather than implanting a ventricular assist device, bi-ventricular pacing devices similar to pace makers may be implanted in some cases, e.g., cases in which a heart beats inefficiently in a particular asynchronous manner. While the implantation of a bi-ventricular pacing device may be effective, not all heart patients are suitable for receiving a bi-ventricular pacing device. Further, the implantation of a bi-ventricular pacing device is expensive, and is generally not effective in significantly reducing or eliminating the degree of mitral regurgitation.
Open-heart surgical procedures which are intended to correct for mitral valve leakage, specifically, can involve the implantation of a replacement valve. Valves from animals, e.g., pigs, may be used to replace a mitral valve 20 in a human. While the use of a pig valve may relatively successfully replace a mitral valve, such valves generally wear out, thereby requiring additional open surgery at a later date. Mechanical valves, which are less likely to wear out, may also be used to replace a leaking mitral valve. However, when a mechanical valve is implanted, there is an increased risk of thromboembolism, and a patient is generally required to undergo extended anti-coagulant therapies.
A less invasive surgical procedure involves heart bypass surgery associated with a port access procedure. For a port access procedure, the heart may be accessed by cutting between ribs or sometimes removing parts of one or more ribs, as opposed to dividing the sternum to open the entire chest of a patient. In other words, the opening occurs between the ribs in a port access procedure, rather than opening a patient's sternum.
One open-heart surgical procedure that is particularly successful in correcting for mitral valve leakage and, in addition, mitral regurgitation, is an annuloplasty procedure. During an annuloplasty procedure, a medical device—an annuloplasty ring—may be implanted surgically on the left atrial side of mitral annulus (the attachment of the base of the mitral valve to the heart) to cause the size of a dilated mitral valve annulus to be reduced to a relatively normal size, and specifically to move the posterior leaflet closer to the anterior leaflet to aid anterior-posterior leaflet coaptation and thus improve the quality of mitral valve closure and significantly reduce the amount of mitral insufficiency. FIG. ID is a schematic representation of an annuloplasty ring 34. An annuloplasty ring 34 is shaped approximately like the contour of a normal mitral valve 20. That is, annuloplasty ring 34 is shaped substantially like the letter “D.” Typically, annuloplasty ring 34 may be formed from a rod or tube of biocompatible material, e.g., plastic, that has a DACRON mesh covering.
In order for annuloplasty ring 34 to be implanted, a surgeon surgically attaches annuloplasty ring 34 to the mitral valve on the atrial side of the mitral valve 20. Conventional methods for installing ring 34 require open-heart surgery which involve opening a patient's sternum and placing the patient on a heart bypass machine. As shown in FIG. 1E, annuloplasty ring 34 is sewn to a posterior leaflet 24 and an anterior leaflet 22 of a top portion of mitral valve 20. In sewing annuloplasty ring 34 onto mitral valve 20, a surgeon generally sews the straight side of the “D” to the fibrous tissue located at the junction between the posterior wall of the aorta and the base of the anterior mitral valve leaflet. As the curved part of the ring is sewn to the posterior aspect of the annulus, the surgeon alternately acquires a relatively larger amount of tissue from the mitral annulus, e.g., a one-eighth inch bite of tissue, using a needle and thread, compared to a relatively smaller bite taken of the fabric covering of annuloplasty ring 34. Once a thread has loosely coupled annuloplasty ring 34 to mitral valve tissue, annuloplasty ring 34 is slid into contact with the mitral annulus 40 such that the tissue of the posterior mitral annulus that was previously stretched out, e.g., due to an enlarged heart, is effectively reduced in circumference and pulled forwards towards the anterior mitral leaflet by the tension applied by annuloplasty ring 34 by the thread that binds the annuloplasty ring 34 to the mitral annulus tissue. As a result, a gap, such as gap 32 of FIG. 1C, between anterior leaflet 22 and posterior leaflet 24 during ventricular contraction (systole) may be reduced and even substantially closed off in many cases thereby significantly reducing or even eliminating mitral insufficiency. After the mitral valve 20 is shaped by ring 34, the anterior and posterior leaflets 22, 24 will reform typically by pulling the posterior leaflet forward to properly meet the anterior leaflet and create a new contact line that will enable mitral valve 20 to appear and to function properly.
Once implanted, tissue generally grows over annuloplasty ring 34, and a line of contact between annuloplasty ring 34 and mitral valve 20 will essentially enable mitral valve 20 to appear and function normally. Although a patient who receives annuloplasty ring 34 may be subjected to anti-coagulant therapies, the therapies are not extensive, as a patient is only subjected to the therapies for a matter of weeks, e.g., until tissue grows over annuloplasty ring 34.
A second surgical procedure which is generally effective in reducing mitral valve leakage associated with prolapse of the valve leaflets involves placing a single edge-to-edge suture in the mitral valve 20 that apposes the mid-portions of anterior and posterior leaflets. With reference to FIG. 1F, such a surgical procedure, e.g., an Alfieri stitch procedure or a bow-tie repair procedure, will be described. An edge-to-edge stitch 36 is used to stitch together an area at approximately the center of the gap 32 defined between an anterior leaflet 22 and a posterior leaflet 24 of a mitral valve 20. Once stitch 36 is in place, stitch 36 is pulled in to form a suture which holds anterior leaflet 22 against posterior leaflet 24, as shown. By reducing the size of gap 32, the amount of leakage through mitral valve 20 may be substantially reduced.
Although the placement of edge-to-edge stitch 36 is generally successful in reducing the amount of mitral valve leakage through gap 32, edge-to-edge stitch 36 is conventionally made through open-heart surgery. In addition, the use of edge-to-edge stitch 36 is generally not suitable for a patient with an enlarged, dilated heart, as blood pressure causes the heart to dilate outward, and may put a relatively large amount of stress on edge-to-edge stitch 36. For instance, blood pressure of approximately 120/80 or higher is typically sufficient to cause the heart 10 to dilate outward to the extent that edge-to-edge stitch 36 may become undone, or tear mitral valve tissue.
Another surgical procedure which reduces mitral valve leakage involves placing sutures along a mitral valve annulus around the posterior leaflet. A surgical procedure which places sutures along a mitral valve 20 will be described with respect to FIG. 1G. Sutures 38 are formed along the annulus 40 of a mitral valve 20 that surrounds the posterior leaflet 24 of mitral valve 20. These sutures may be formed as a double track, e.g., in two “rows” from a single strand of suture material 42. Sutures 38 are tied off at approximately a central point (P2) of posterior leaflet 24. Pledgets 44 are often positioned under selected sutures, e.g., at the two ends of the sutured length of annulus or at the central point P2, to prevent sutures 38 from tearing through annulus 40. When sutures 38 are tightened and tied off, the circumference of the annulus 40 may effectively be reduced to a desired size such that the size of a gap 32 between posterior leaflet 24 and an anterior leaflet 22 may be reduced.
The placement of sutures 38 along annulus 40, in addition to the tightening of sutures 38, is generally successful in reducing mitral valve leakage. However, the placement of sutures 38 is conventionally accomplished through open-heart surgical procedures. That is, like other conventional procedures, a suture-based annuloplasty procedure is invasive.
While invasive surgical procedures have proven to be effective in the treatment of mitral valve leakage, invasive surgical procedures often have significant drawbacks. Any time a patient undergoes open-heart surgery, there is a risk of infection. Opening the sternum and using a cardiopulmonary bypass machine has also been shown to result in a significant incidence of both short and long term neurological deficits. Further, given the complexity of open-heart surgery, and the significant associated recovery time, people who are not greatly inconvenienced by CHF symptoms, e.g., people at a Class 1 classification, may choose not to have corrective surgery. In addition, people who most need open heart surgery, e.g., people at a Class 4 classification, may either be too frail or too weak to undergo the surgery. Hence, many people who may benefit from a surgically repaired mitral valve may not undergo surgery. FIG. 1H illustrates the cardiac anatomy, highlighting the relative position of the coronary sinus (CS) 46 running behind the posterior leaflet 24 of the mitral valve 20. FIG. 1I is an illustration of the same anatomy but schematically shows a cinching device 48 which is placed within the CS 46 using a catheter system 50, with distal, mid, and proximal anchors 52a, 52b, 52c within the lumen of the CS 46 to allow plication of the annulus 40 via the CS 46. In practice, these anchors 52a-c are cinched together, i.e., the distance between them is shortened by pulling a flexible tensile member 54 such as a cable or suture with the intent being to shorten the valve annulus 40 and pull the posterior leaflet 24 closer to the anterior leaflet 22 in a manner similar to an annuloplasty procedure. Unfortunately, since the tissue which forms the CS 46 is relatively delicate, the anchors 52a-c are prone to tear the tissue during the cinching procedure, and the effect on the mitral annulus may be reduced by the position of the coronary sinus up more towards the left atrium rather than directly over the mitral annulus itself. Other minimally invasive techniques have been proposed and/or developed but have various drawbacks related to such factors as effectiveness and/or cases and accuracy of catheter-based implementation.
Therefore, there remains a need for improved minimally invasive treatments for mitral valve leakage. Specifically, what is desired is a method for decreasing the circumference of the posterior mitral annulus, moving the posterior leaflet forwards towards the anterior leaflet and thereby reducing leakage between an anterior leaflet and a posterior leaflet of a mitral valve, in a manner that does not require conventional surgical intervention.